This invention relates to a method of manufacturing a cold cathode device which has a porous portion, for example, a porous silicon portion, as an emitter portion. Such cold cathode can be fabricated in a flat display, a cathode ray tube (CRT), an electron microscope, an electron beam (EB) lithography apparatus, and EB sources for use in various kinds of EB apparatuses.
A field emission cold cathode is manufactured by using a technology of semiconductor minute processing. With the rapid development of the technology, the field emission cold cathode comes to have a high performance and might be expected to be substituted for a conventional cathode device.
Various kinds of proposals have been made about the cold cathode devices, in order to improve performance of the devices. One of them has a porous portion as an emitter portion. In such cold cathode, when a voltage is given between an emitter substrate having the emitter portion and a gate electrode of the cold cathode, the voltage generates an electrical field, which concentrates on the porous portion, because of high resistance of the porous portion. The concentrated field let the porous portions emit electrons, efficiently.
Such cold cathode devices with porous emitters are disclosed in, for example, JP-A Nos. 8-87956, 8-250766, 9-237567, and 9-259795, which will be referred to as conventional techniques. Furthermore, the conventional techniques also teach us various methods of manufacturing the cold cathode devices with porous emitters, in each of which anodic etching process is executed to render the silicon portion into the porous emitters.
However, these conventional techniques have a disadvantage that the conventional techniques can not always provide even quality of the emitter portions. In detail, n-type silicon is selected as a material of the emitter substrate in every conventional technique, because the n-type substrate can emit the electron without saturation. This n-type substrate should be subjected to irradiation during the anodic etching, in order to promote a reaction of the anodic etching. Good reaction makes the porous pretty fine. On the other hand, electron emission depends on thickness of the porous silicon and size of fine crystal comprising the porous silicon, and they are influenced by the irradiation. These means that the uniform electron emission can not be obtained, if the irradiation is not executed uniformly. In spite of this, the irradiation according to the conventional technique is not always uniformly executed, and makes the quality of the porous in the emitter portion uneven.
For example, JP-A 8-87956 uses two electrode plates only for anodic etching to form the porous emitter. The electrode plates are made of metal material, such as platinum (Pt), and have characteristics of blocking off light emitted from light source. As the results, the light source irradiates silicon portion from an inclined direction with respect to a gate electrode of the cold cathode device, in JP-A 8-87956. Such inclined irradiation brings about uneven quality into the emitter portion, because the silicon portion can not be subjected to a uniform irradiation.
There is an anodic etching technique known to the inventor that uses the emitter substrate instead of an anodic one of the foregoing electrode plates. Such technique also causes the above-mentioned inclined irradiation, resulting in bringing about the same problem. Furthermore, the other conventional techniques may employ either one of the foregoing anodic etchings and, in this event, can not prevent the uniform irradiation.
This invention therefore provide a method of manufacturing a cold cathode, in which an anodic etching is executed with a uniform irradiation for a predetermined silicon portion, and can obtain a desirable porous silicon portion.
According to one aspect of the present invention, a method for manufacturing a cold cathode device which has a porous silicon portion as an emitter portion, is obtained. Such method includes the following processes. First, an object that comprises a silicon layer, a gate electrode, and an insulator layer interposed between the silicon layer and the gate electrode, is formed. Herein, the gate electrode has a gate aperture, while the insulator layer has a through-hole corresponding to the gate aperture. The silicon layer has a predetermined portion exposed inside the through-hole.
And then, a part of the object is soaked into an electrolytic solution, so that both the through-hole and the gate aperture are filled with the electrolytic solution. Under the circumstances, the silicon layer is given an electric potential, while the gate electrode is given an electric potential lower than that of the silicon layer. And thereby, the predetermined portion is subjected to anodic etching to be rendered into the porous silicon portion. That is, in this anodic etching, the silicon layer serves as an anode electrode, while the gate electrode serves as a cathode electrode. Such anodic etching changes the object into the cold cathode device with the porous silicon portion.
The silicon layer may be made of n-type silicon. In this case, the above-mentioned method may further comprise irradiating the predetermined portion through both the through-hole and the gate aperture from a vertical direction with respect to the gate electrode, during the giving the electric potential to the silicon layer.
With such processes, the manufacturing method does not require an electrode plate only for anodic etching. In addition, the predetermined silicon portion is irradiated from the vertical direction with respect to the gate electrode, and therefore, the irradiation is executed uniformly for the predetermined silicon portion to change it into the desirable porous silicon portion.